Sitting All Day: Worse For You Than You Might Think04:17

Most Americans spend the majority of their waking hours sitting still in front of a computer or television. (iStockphoto.com)

Yes, exercise is good for you. This we know. Heaps of evidence point to the countless benefits of regular physical activity. Federal health officials recommend at least 30 minutes of moderate exercise, like brisk walking, every day.

Studies show that when you adhere to an exercise regimen, you can improve your cardiovascular health, lower blood pressure and improve metabolism and levels of cholesterol and triglycerides. You can reduce diabetes risk and the risk of certain cancers. And, finally, exercise can help you maintain a healthy weight, which can boost all of these benefits even more.

But now, researchers are beginning to suspect that even if you engage in regular exercise daily, it may not be enough to counteract the effects of too much sitting during the rest of the day.

Epidemiologist Steven Blair, a professor of public health at the University of South Carolina, has spent 40 years investigating physical activity and health.

"Let's say you do 30 minutes of walking five days a week (as recommended by federal health officials), and let's say you sleep for eight hours," Blair says. "Well, that still leaves 15.5 hours" in the day.

Many of us, he points out, have sedentary jobs and engage in sedentary activities after work, like watching television or sitting around a dinner table talking. When you add it all up, Blair says, "it's a lot more sitting than moving."

Blair recently headed a study at the University of South Carolina that looked at adult men and their risk of dying from heart disease. He calculated how much time the men spent sitting — in their cars, at their desks, in front of the TV.

"Those who were sitting more were substantially more likely to die," Blair says.

Specifically, he found that men who reported more than 23 hours a week of sedentary activity had a 64 percent greater risk of dying from heart disease than those who reported less than 11 hours a week of sedentary activity. And many of these men routinely exercised. Blair says scientists are just beginning to learn about the risks of a mostly sedentary day.

"If you're sitting, your muscles are not contracting, perhaps except to type. But the big muscles, like in your legs and back, are sitting there pretty quietly," Blair says. And because the major muscles aren't moving, metabolism slows down.

"We're finding that people who sit more have less desirable levels" of cholesterol, blood sugar, triglycerides and even waist size, he says, which increases the risk of diabetes, heart disease and a number of health problems.

'Our Body Just Kind Of Goes Into Shutdown'

Dr. Toni Yancey, a professor in the health services department and co-director of the Kaiser Permanente Center for Health Equity at the University of California, Los Angeles, has worked for years on developing programs to motivate people to get up and move.

"We just aren't really structured to be sitting for such long periods of time, and when we do that, our body just kind of goes into shutdown," Yancey says.

She recommends routine breaks during a full day of sitting. Her book, Instant Recess: Building a Fit Nation 10 Minutes at a Time, offers readers a guide to integrating such activity into the corporate boardroom, school classroom and even at sporting events.

But even if your work site doesn't engage in routine hourly breaks, there are things individuals can do at their desks to break up a day of inactivity and get moving, even if just for a few minutes. Yancey recommends a few minutes of movement every hour.

And she suggests sitting on an exercise ball instead of a desk chair, adding that it helps strengthen the core while improving balance and flexibility. It also requires more energy, so a few calories will be burned.

It may not sound like much, but an Australian study found that these types of mini-breaks, just one minute long throughout the day, can actually make a difference. You can simply stand up, dance about, wiggle around, take a few steps back and forth, march in place. These simple movements can help lower blood sugar, triglycerides, cholesterol and waist size.

"If there's a fountain of youth, it is probably physical activity," says Yancey, noting that research has shown benefits to every organ system in the body.

"So the problem isn't whether it's a good idea," she says. "The problem is how to get people to do more of it."